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12 volt battery insurance/backup plan

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M3noob

Active Member
Supporting Member
Aug 22, 2019
1,065
819
Beyond the pale
As I spend a fair number of thousand kilometers in foreign parts and rue the limitations of Tesla's roadside empty promises, I bought a 12 V battery from Europarts. Good price as they are having a mid-year sale of sorts. I got a four year warranty which seems to be a lot better performance than the one that Tesla fits that seems to die after two years. Having passed my 3's second birthday, I thought it wise to gird myself.

The sucker is heavy (being full of lead explains a lot) but a much much lighter drain on the bank balance than a svelt lithium battery.

I also carry a MN23 battery for popping the frunk and a lithium jumper battery just in case I can persuade the OEM 12 volt battery to get me rolling to somewhere convenient apres message of impending doom.

Shown is the Varta I chose: not the cheapest, not the most dear. £77, a hair cheaper than one from the Service Centre (if in stock). Available by Click and Collect.

Yeah, I know I am sapping my efficiency by tenths of a percent by lugging all that kit around but it beats living through the nightmare inflicted on other elements of this hive mind.

PXL_20220620_131050636.jpg


Also shown is another example of my low regard for Tesla Roadside (dis)service: a Road Hero spare. It got me back from France one Sunday when neither AA or Tesla CBA.
 
It's 1700 km between my UK and my Spanish base, a lot of it in the emptiest bits of France. Are you going to come rescue me if the battery goes pffft? I didn't think so.

I was never a Boy Scout but their motto makes a lot of sense if you drive a two year old Tesla.
Just replace to new battery every year or two.

HV (main) battery will top up / charge your 12 v battery once in a while when needed.

This is just too much imho... Did you carry your spare battery in your ICE car? In case, you know, alternator dies?
 
Under the normal run of things the 12v should only die if there is a catastrophic failure. The car monitors the 12v and wakes itself up to charge it when it needs topping up, and if it detects that this is happening too often it deems it has worn out, at which point the car won't sleep anymore as it will be providing 12v backup constantly.

If/when there is a catastrophic failure of the 12v, to the point where the car doesn't find out about it before there's not enough power to wake itself up, then a battery monitor wouldn't help you there anyway.

Carrying a spare 12v battery is an interesting one. I've never thought about it in previous cars. I wonder whether it would be enough just to have a 12v booster on hand, enough to get the 12v alive and kicking again for the car to take over management of it?
 
Think it would be better to just replace your 12v with the new one you've bought every two years if it concerns you. If you're lugging it round in the boot, does it still have both bungs in the vent holes? Worth checking regularly to make sure they don't pop out, especially when you're in Spain. The heat in the car when parked could cause enough pressure rise to push one out. Sulphuric acid will make a mess of your boot tray.

The BM2 battery monitor looks good, as per Kelvin's post above. Andrew Till (Mr EV) did a good video on it recently - he fitted it to his Ioniq 5.
 
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wow that's pretty excessive. The car does alert if it detects an anomaly with the battery, which should happen before any failure. Also a jump pack should get the car started again in an emergency and then the internal charge circuits should keep things running unless there's like a hole in the battery or something .... If you really are worried about the quality of the supplied battery, just pull it out and stick a 5 year warranty battery (like a bosch) in and forget about it.
And this is coming from someone with a 7 year old Leaf, which are renowned for crap batteries.
 
ITT: lots of people who have never had their 12v flunk on them. I don't blame you for doing this one bit especially over those distances in Europe. 😂

The 12v bms and associated warnings are not impervious to errors or flaws. Namely, duff batteries can throw all the clever stuff for a loop completely. Ask me how I know.

I'd do the same with your driving pattern and vehicle circumstances noob.
 
I always thought the car gave you a "12v battery needs replacing" or equivalent message, or the battery failed after the car had been left a while and so nobody there to see the message if the car detected the fault. I imagine a spare tyre would be the first thing to carry before a 12v battery in your situation, maybe you do that too?

As an aside, anyone thinking of doing this, since 2022 most cars now don't have this type of battery.
 
ITT: lots of people who have never had their 12v flunk on them. I don't blame you for doing this one bit especially over those distances in Europe. 😂

The 12v bms and associated warnings are not impervious to errors or flaws. Namely, duff batteries can throw all the clever stuff for a loop completely. Ask me how I know.

I'd do the same with your driving pattern and vehicle circumstances noob.
but again, isn't it better to opt for new li-on 12v battery or just replace existing type to new every year and that's it?! It's quite silly to carry additional weight in frunk for just in case. I mean I am sure you should be able to buy 12 v battery in France?
again - did you ever carried spare battery in your previous cars? just in case your alternator dies and it will chump though your battery? definitely not.

I remember when the tread on failed battery by Mr MIserable caused lots of oohs and aaahs, but this was caused by another, much more serious problem with his main battery, and 12v was just a consequence. If your 12v fails - then you have much more serious problems...
 
I always thought the car gave you a "12v battery needs replacing" or equivalent message,
I think the issue is that the window between this message being triggered and complete failure is sometimes around a day. I'm tending to think more along the lines of preemptive replacement though since the cost is probably 1 year in 4 of the replacement battery (with the added hassle of charging every 6 months)
 
Should you even use a wet cell battery in a Tesla? I'm assuming the charging characteristics differ from a lithium battery and as such might cause problems? As a temporary measure - sure... but at that point you'll need to replace with a lithium battery asap anyways?
 
Should you even use a wet cell battery in a Tesla? I'm assuming the charging characteristics differ from a lithium battery and as such might cause problems? As a temporary measure - sure... but at that point you'll need to replace with a lithium battery asap anyways?
older ones, pre 2022, were delivered with old style, wet cell lead batteries.

New cars are delivered with li-on batteries.
 
but again, isn't it better to opt for new li-on 12v battery or just replace existing type to new every year and that's it?! It's quite silly to carry additional weight in frunk for just in case. I mean I am sure you should be able to buy 12 v battery in France?
again - did you ever carried spare battery in your previous cars? just in case your alternator dies and it will chump though your battery? definitely not.

I remember when the tread on failed battery by Mr MIserable caused lots of oohs and aaahs, but this was caused by another, much more serious problem with his main battery, and 12v was just a consequence. If your 12v fails - then you have much more serious problems...
Covering those distances in a car with the original (old-style) battery, it's not silly at all if you don't want the inconvenience of a battery lockout.

I'd do the same thing for long trips if I still had my Model S and was doing 1000+ miles across Europe regularly.

Not worried about my model Y battery at all in the same way, but the 12v went on my Model S and it was a huge PITA. Killed other components which were very expensive, left me without a car for days, made it a nightmare for tow recovery and it happened without warning, and just a few weeks after the car had a full service at Tesla where they tested both the HV and LV system. I would proactively change the battery every year to avoid that again if I had to.

So I'd just say don't be surprised people will go to lengths to avoid the potential for having to deal with that in the middle of the continent. The weight really isn't that big of a deal if you're travelling.
 
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Carrying an MN23 to break into the car sounds pretty sensible, but where? I also have a print of the manual pages of how to use the mini leads to pop the frunk in a dead battery situation, but they, like the battery, would be in the rear centre console.

If the 12v goes you can't get into the car, can you? So my instructions for how to, and the battery to do it with are in the locked car? Should I strap both to the inside of the tow bar cover so they can be accessed?

Overall tho, I think I'd go for just replacing the main 12v battery rather than carrying a spare? My car is coming up to 3 years, so may add that to the pre-first MOT list along with brakefluid etc.